eek! Thanks for spotting that one!
After the questionnaire gets submitted the page is redirected to a sort of "thank you" page which basically says thanks and provides a couple of interesting links.
Recently I changed the directory that I was keeping the web site in ...but I forgot to update the link to the thank-you page!
Despite the ominous error message, the questionnaire would have been sent successfully. I have now fixed the error...thanks for your help!
Next time I'll remember to test the site first - lesson learnt!
thanks again
Si.